Field of the Invention
The present invention relates generally to electric power systems and electrostatic and electromagnetic fields associated with high voltage fields; more particularly the invention relates to X-ray radiation in such fields, which is suspect in the etiology of leukemia and other forms of cancer. Health hazards to persons from prolonged exposure to such fields are eliminated by preventive systems and equipment shielding according to the invention.
For several years studies have indicated a strong statistical relation between various childhood cancers and proximity of persons to high tension power lines. A Johns Hopkins University study by S. J. London et al. showed an especially high correlation of cancers to extremely high voltage lines. This study was done by comparing the utility power configurations associated with childhood leukemia with a random sampling of people in the Los Angeles area. It showed two to three times higher occurrence of high power lines in the vicinity of the leukemia patients than for the general public. Other studies have shown an occurrence of breast cancer in male power line workers approximately four times that of the general public.
Because of such studies, power companies have been attempting to ascertain a causal relation between the presence of power lines and the health effects. When the locations studied in the Johns Hopkins University study were checked for electric field strength--i.e., electric and magnetic fields, no correlation was found. Despite the lack of correlation to electric field strength or magnetic field strength, reduction of these fields has been the primary focus of the power companies, for lack of more definitive approaches.
Certain relevant technical aspects are well known in the art. The electric field surrounding a low frequency conductor is approximately perpendicular to the surface of the conductor, as with power lines with corona discharge, and field strength increases near small radii. The equipotential lines are parallel to the conductor and the gradient is perpendicular to the surface in the vicinity of the surface. The wavelength at 60 Hz is sufficiently long with respect to the ionization zone around the conductor to ignore the component in the direction of the conductor. The high electric field provides the energy to accelerate the free electrons to sufficient energy levels to generate X-rays. Soft X-ray levels are only 2-10 times the energy of hard ultraviolet UV, and continue up from there.
Extraneous electric and magnetic fields, which were thought to be a health risk associated with electric power transmission, were avoided in the prior art by using various cable and wiring arrangements, particularly coaxial transmission lines configured so that return current flows in the outer conductors in a bi-polar field-cancelling mode particularly suited to reducing electromagnetic fields. See U.S. Pat. No. 5,218,507 to Ashley, June 1993. However, little attention has been given to X-rays caused by high voltage fields accelerating electrons in coronas. It has been believed that X-rays produced thereby are too soft to be of concern. Recently, there have been statistical studies of correlations of cancer cases with the possibility of X-ray generation in power plants in the vicinity of patients' normal activity. See IEEE Transactions on Broadcasting, Vol. 36, No. 1, March 1990.